Countercurrent flow centrifugal exchangers



Dec. 7, 1965 J. w. BURDETT 3,221,985

COUNTERCURRENT FLOW GENTRIFUGAL EXCHANGERS Filed June 13, 1961 2 Sheets-Sheet l i 460 =2 34e 34b 34d 340 2 540 a I g! s 5 FIG. 4

INVENTOR:

J. W. BURDETT BYI HIS ATTORNEY FIG.3

Dec. 7, 1965 J. w. BURDETT 3,22

COUNTERGURRENT FLOW GENTRIFUGAL EXCHANGERS Filed June 13, 1961 V 2 Sheets-Sheet 2 FIG.2

INVENTORI J. W. BURDET T HIS ATTORNEY United States Patent O 3,221,985 coUNrnRcUuunNr FLOW CENTRIFUGAL EXCHANGER Joseph W. Burdett, Houston, Tex., assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed June 13, 1961, Ser. No. 116,752 6 Claims. (Cl. 233-15) The invention relates to improvements in countercurrent-flow, centrifugal exchange devices of the type wherein principal fluids of different densities which are at least partially immiscible with one another flow in opposed radial directions through perforations in partition walls which surround the axis of rotation of a rotor, and in the method of effecting such a countercurrent exchange wherein an auxiliary fluid is introduced. The purpose of such countercurrent exchange is to subject one fluid to the solvent action of the other, thereby to wash or extract a constituent or group of constituents. For example, such devices are used in the solvent refining of petroleum fractions, e.g., in extracting oil with phenol or furfural, and in the purification of chemicals and pharmaceuticals. Usually both fluids are liquid but in some application the one of lower density may be a gas or vapor.

More particularly, the instant invention is concerned with means for admitting an auxiliary fluid to the exchanger, e.g., an anti-solvent such as water, to modify the properties of the fluids and/or alter the solubility relations.

Known centrifugal countercurrent exchangers comprise a cylindrical rotor casing mounted for rotation on a shaft and containing a plurality of radially spaced, perforated partition walls which surround the shaft substantially concentrically, i.e., which are concentric cylinders or which form a continuous spiral the turns of which the so closely spaced as to function practically as cylinders. Means, e.g., ducts communicating through the shaft, are provided for admitting the raw fluids to and discharging the contacted fluids from the rotor interior at different radial distances from the rotor shaft. Typically, the partition walls are spaced radially about 0.2 to 3 inches by the use of spacers or indentations or dimples. When the rotor is spun at 500 to 5,000 r.p.m. the centrifugal forces developed far exceed the force of gravity, so that the latter force has a negligible influence on the flow of fluids inside the rotor. The apparatus, therefore, acts in a manner analogous to a gravity-flow perforated plate extraction column without downcomers or risers, the region near the shaft corresponding to the top of such a column.

It is known to introduce a third fluidherein called the auxiliary fluidinto the rotor in addition to the principal fluids. For example, water is sometimes admitted as auxiliary liquid when lubricating oil is extracted with phenol to generate reflux liquid. (See, for example, the US. Patent No. 2,857,326, dated October 21, 1958, to Benedict.) Due to the complexity of the arrangements for supplying fluids to the rotor it is customary to introduce such an auxiliary fluid together with the principal fluid with which it is immiscible in the form of a dispersion. As an example, water is admitted with the oil, it reduces the solvent power of the phenol at the stage at which the fresh oil and final extract phases are in contact.

More efficient use of the reflux formed by the auxiliary liquid would result if it were introduced at some stage ice other than the feed stages for the principal fluids, e.g., into a stage intermediate the said feed stages or beyond it.

It is the object of this invention to provide an improved method and apparatus for effecting centrifugal countercurrent exchange of principal fluids in a series of stages wherein an auxiliary fluid which is introduced into a contacting stage other than the feed stages to which the principal fluids are charged Without providing a separate inlet passageway leading into the rotor.

In summary, according to the invention the auxiliary fluid is introduced into the rotor in admixture with one of the principal fluids with which it is immiscible therewith, separated centrifugally therefrom within the rotor, and introduced from the separating zone into a contacting stage other than that to which the said principal fluid is introduced.

The invention can be applied either in the case where the auxiliary fluid is introduced in admixture with the lighter or with the heavier principal fluid; only the former case will be described herein. In the former instance the principal and auxiliary fluids are introduced from the separating zone to radially outer contacting stages, while in the latter they are introduced into stages near the rotor axis.

The invention will be further described with reference to the accompanying drawings forming a part of this specification and showing one perferred embodiment, wherein:

FIGURE 1 is a diagrammatic perspective view of a centrifugal exchanger device, parts being broken away and stationary parts being shown in dashed lines;

FIGURE 2 is an axial sectional view through the rotor;

FIGURE 3 is a fragmentary, enlarged transverse sectional view showing a part of FIGURE 2 on an enlarged scale; and

FIGURE 4 is a sectional View corresponding to FIG- URE 3 and showing a modification.

It will be understood that, throughout, the drawings are partly diagrammatic in that the number of partition walls and holes shown are less than would usually be used and that the dimensions are altered for clarity.

Referring to FIGURES 1-3, the contactor comprises a supportion framework 11 which carries a rotatable shaft 12 upon which is mounted a rotor 13. As shown in dotted lines in FIGURE 1, the rotor has a stationary casing comprising upper and lower sections 14 and 15. Torque for driving the rotor is applied to a drive pulley 16. The shaft 12 has two axial bores which are interrupted at the rotor and contain smaller coaxial pipes 17 and 18, respectively, to define four channels: a pair of supply channels within the pipes 17 and 18 for the influx to the rotor of the heavier and lighter fluid, respectively, and annular channels 19 and Zll for the eiflux of contacted lighter and heavier fluids, respectively. The inlet ends of the pipes 17 and 18 communicate through bores in stationary caps 21 and 22 at the extremities of the shaft with inlet openings 23 and 24, respectively, suitable sealing means being provided at 25 and 26 to isolate the inflowing fluids from the outflowing fluids. Outlet pipes 27 and 28 communicate with the annular channels 19 and 20, respectively.

The rotor 13 comprises a hub 9 which is fixed to the shaft 12, and a rotor housing which includes a pair of annular end plates 29 and 30 fixed to the hub and a peripheral wall 31 to define a closed chamber. Within the rotor and spaced from the end plates with a small clearance sufiicient to provide flow spaced adjacent the plates 29 and 30 are interior annular end plates 32 and 33 which are joined to the hub and terminate radially short of the wall 31. A plurality of concentric perforated partition walls 34 (sometimes identified with letter suffixes) is mounted in radially spaced relation between the interior end plates to define a plurality of annular contacting compartments situated at progressively increasing radii. The radial dimensions of such spaces are typically between 0.2 and 3 inches. Fresh heavier fluid from the pipe 17 is admitted to a contacting compartment at a radially inner part of the rotor but preferably not the innermost compartment by one or more radial tubes 35 and a passage 36 formed in the shaft. These tubes extend through holes in the inner partition wall with close fits. Contacted lighter fluid flows from the space immediately surrounding the hub 9 into the annular channel 19 via one or more ports 37 formed in the hub and shaft 12. Fresh lighter fluid, together with an auxiliary fluid, flows to one or more centrifugal separating chambers 38 from the pipe 18 via a corresponding number of passages 39 drilled in the shaft, for introduction to radially outer compartments as will be described. Contacted heavier fluid flows from the space immediately adjoining the peripheral wall 31 through a radial passage 40 situated between the end plates 30 and 33 and a similar passage 40a between the end plates 30 and 33, and thence via registering ports in the hub 9 into passages 41 and 41a formed in the shaft. Flow from the passage 40 is further through an axial passage 42 milled into the hub. Vanes 43 extending generally radially but curved like turbine blades may be provided within the passages 40 and 40a to aid in reducing the circumferential velocity of the fluid which moves radially inward, but may be omitted.

The partition walls 34 have perforations of any known or suitable form, such as the perforations 44 shown in FIGURE 3, it being evident that this invention is not restricted to any specific arrangement or shapes of these openings. For example, these may be formed as two sets, for the separate flows of the two phases, while presenting negligible pressure drop to the continuous phase, as is disclosed in the copending application of instant applicant and Kenneth E. Train, Serial No. 116,827, filed June 13, 1961. Also, although only one radial feed tube 35 and one centrifugal separating chamber 38 are illustrated, any number of these elements may be used, arranged to attain static and dynamic balance in the rotor to permit vibrationless operation at high speed.

The wall of the chamber 38 has lateral passageways 45 and 46 situated at different radial distances from the shaft to discharge feed fluids into desired compartments. As shown, each of these may be formed as a plurality of side ports. For example, the ports forming the passage- Way 45 may communicate with the contacting compartment 47 between the two outmost partition walls 34a and 3412 while the passageway 46 is situated to discharge fluid into the compartment 48 between partition walls 34:! and 342. In the embodiment shown it is desirable to restrict the passageways 46 and to provide a large passageway 45; the purpose of this will become apparent. A deflector plate, formed in this illustrative embodiment as a sleeve 49, is sealed to the tube wall between the passageway 46 and the inlet or radially inner end of the tube 38 and extends opposite this passageway and beyond it in spaced relation to the tube wall to define an annular channel 50.

As applied, for example, to the solvent extraction of a lubricating oil stock with phenol as a selective solvent for constituents of the oil, the latter is admitted through the pipe 17 and a dispersion of oil and water is supplied through the pipe 18, both under suitable pressures, and the rotor is turned on its shaft. The oil-water dispersion flows radially outwards through the tube 38 and is centrifugally separated as is shown in FIGURE 3 to form a layer of water 51 below an interface I. A body of oil collects within the channel 59. The separated water and oil enter the compartments 47 and 48 through the passageways 45 and 46, respectively. The deflector 49 prevents direct efi'lux of the oil-water dispersion through the latter passageway.

Various arrangements may be used to regulate the separate efflux of oil and water from the separating chamber. In that illustrated herein the passageway 45 is unrestricted and large enough to produce a negligible pressure drop to flow of water into the reflux section of the rotor. The ports forming the passageway 46 are restricted to limit the flow rate to the rate at which oil is charged to the rotor through the pipe 18.

A pressure head exists across the oil passageway 46 which is equal to the product of: (l) the radial distance between the two passageways 45 and 46, (2) centrifugal force and (3) the difference between the average density of the liquid outside the separating chamber and the average density of the liquid inside the chamber between these passages. (It is assumed that the holes 45 do not impose a significant pressure drop; when this is not the case the pressure drop developed must be subtracted from the said product. It is also assumed that the liquid phase outside the separating chamber is continuous with no significant pressure drop due to restrictive fiow as it moves from compartment 43 (FIGURE 3) to compart- 47; when this is not the case the pressure drop attributed to restrictive flow must be subtracted from the said product.) This pressure head will vary as the radial location of the Water-oil interface I varies, as it determines the average density of the liquids within the separating chamber. Maximum pressure head is obtained when the interface is at the Water outlet 45, and a minimum head prevails when the level is at the oil outlet. Because the velocity of oil flow through the latter is a function of orifice pressure drop, an orifice area can be chosen to give a range of oil flow rates to accommodate normal operation at design flow rates of the various feed stocks. Water flow does not affect the design of the centrifugal separating chamber and its outlet provided, of course, that the rate of water flow does not exceed the settling capacity of the chamber.

Major changes in oil charge rates are normally associated with changes in rotor speed; this changes the centrifugal force and shifts the operating range of the oil outlet in the direction of the flow rate change.

The oil and solvent flow countercurrently through the several contacting compartments between the walls 34, passing through the holes 44. The raflinate, consisting principally of oil, is discharged via the ports 37 and channel 19. The compartments radially outwards from 48 constitute the reflux section. The solvent phase, which contains the extracted oil constituents in solution and is sometimes called the solvent extract phase, moves from the compartment 48 to the compartment 47 is mixed with water in the latter, reducing the solvent power of the phenol and causing some of the dissolved, extracted oil constituents to be released as reflux. The latter moves radially inwards. The final solvent extract phase from the compartment immediately inside the peripheral wall 31 is discharged through passages 40 and 40a, 41 and 41a, and the channel 26.

FIGURE 4 shows a modification by which it is possible to vary the compartment to which the oil is charged and/or to alter the area of the oil passageways 46. The separating tube 38:: has large ports constituting the water passageway as before; however, it has a plurality of ports 46a, 46b, 46c, 46d communicating respectively with different contacting compartments. Within the tube 38:: is a rotatable valve tube 52 within which the deflector 50 is mounted and having a plurality of large ports 53 for registry with the ports 45 and a plurality of smaller ports 54a, 54b, 54c, 54d, displaced axially for registration with the ports 46a-46d but angularly displaced so that only one is in registration at any particular orientation of the inner tube. Thus, as shown, only the ports 54d and 46d are in registration. The ports 53 are positioned so that the passageway 45 is always open. The end of the inner tube has a flanged end plate 55 which fits within a recess in the outer rotor wall 31 and is secured in place by a threaded plug 56. To secure the inner tube against rotation the touching annular surfaces of the flange 55 and the wall 31 may be provided with suitable locking means, such as radial serrations indicated at 57.

It is evident that the compartment into which the oil is discharged can be con-trolled by adjusting the orientation of the tube 52; in the embodiment shown this is achieved without altering the compartment which receives the water. Because the tube 52 is readily replaceable it is easy to substitute one having oil discharge ports of a suitable size for any prevailing rate of oil flow. This can be dones even if the feature of providing a plurality of oil outlet ports along the lengths of the tubes is not used.

The foregoing example described a case in which the auxiliary fluid (water) was fed to the extractor in admixture with the lighter principal fluid (oil) and the auxiliary fluid had a density intermediate that of the admixed principal fluid and the phase outside the separation which flows in a direction opposite to that of the said admixed principal fluid (the extract phase, consisting principally of phenol). The last-mentioned phase is, for brevity because it is external to the separator tube, called the external phase. These relations are not, however, restrictive of the invention. Thus, when the solvent has a lower density than the liquid being extracted the anti-solvent could be charged in admixture with the heavier principal fluid; the separator would then be situated to discharge into stages near the rotor axis. Further, the density of the auxiliary fluid may be the same as that of the external phase, or the density of the external phase may be intermediate those of the auxiliary fluid and the admixed principal fluid. In this latter case, the interfacial level within the separating chamber is self-regulating in accordance with the densities, and it is not necessary to restrict the passageway 46.

The device would not operate as described if the admixed principal fluid density were intermediate to those of the auxiliary fluid and the external phase; however, it would still be operative to introduce the auxiliary fluid into a stage between those to which the two principal fluids are charged.

I claim as my invention:

1. In centrifugal apparatus for the countercurrent exchange of at least partially immiscible principal fluids of different densities, the combination of:

(a) a rotor including an enclosing wall and an axial shaft mounted for rotation,

(b) a plurality of spaced partition walls within said rotor extending annularly about said shaft and defining a series of contacting compartments siutated at progressively different distances from said shaft, said partition walls having passages therethrough whereby said compartments are in intercommunication,

(c) a wall structure within said rotor defining a centrifugal separating chamber which extends radially throughout a plurality of said intercommunicating compartments,

(d) means communicating with the outside of the rotor and with the interior of said chamber for supplying a mixture of one of said principal fluids and an auxiliary fluid which is substantially immiscible therewith and has a different density from outside the rotor to said separating chamber for separation of the mixture therein by centrifugal force,

(e) separate outlet passageways from said separating chamber communicating with the interior of said chamber at different radial distances from said shaft for the separate discharge from the chamber of the separated principal and auxiliary fluids, said passageways being respectively further in communication with separate, intercommunicating contacting compartments situated at different radial distances from said shaft,

(f) means communicating with the interior and exterior of said rotor for supplying another principal fluid from outside the rotor to a contacting compartment other than those mentioned in (e), and

(g) separate discharge means communicating with interior and exterior of the rotor for discharging respectively the less dense fluid from the rotor interior near the radially inner portion thereof and the denser fluid from the rotor interior near the radially outer portion thereof.

2. Apparatus as defined in claim 1 wherein the said outlet passageways for the auxiliary fluid are substantially unobstructed for the free flow of one separated fluid therefrom and includes means restricting the other passageway to impose a pressure drop to the flow of said one principal fluid.

3. Apparatus as defined in claim 1 wherein the said wall enclosing the centrifugal separating chamber extends through a plurality of said compartments and has a plurality of passageways distributed along the length of the wall and communicating respectively with different compartments; and valve means associated with at least some of said passageways for opening or closing selected ones of said passageways thereby controlling the stages into which at least one of said separated fluids is introduced.

4. Apparatus according to claim 3 wherein said enclosing Wall is a first tube having ports which constitute the said passageways; and said valve means includes an inner tube rotatably mounted within said first tube having a series of ports angularly displaced so that each can be individually brought into registry with one of the ports in the first tube while the others are out of registry.

5. Apparatus as defined in claim 1 wherein the said centrifugal separating chamber has an inlet opening at one radial extremity thereof to which the said means for supplying the mixture is connected, the first outlet passageway, for one of the separated fluids, being situated remotely from said inlet opening and the second outlet passageway, for the other fluid being situated intermediate said inlet opening the first-mentioned outlet passageway; a deflector baflle situated within said separating chamber and connected to said wall structure between said inlet opening and the second outlet passageway, said batfle extending from its connection beyond said second passageway toward the first passageway in spaced relation to the tube wall and defining on the baflle away from said sec ond passageway a channel for the flow of said mixture from the inlet opening into a region of the tube beyond the baflie in isolation to said second passageway, both said passageways being in direct communication with the said region.

6. Apparatus as defined in claim 1 wherein the said wall of the centrifugal separating chamber is formed as a tube and extends radially with respect to the shaft, said tube having an inlet opening at one radial extremity there of to which the said means for supplying the mixture is connected, the first outlet passageway, for one of the separated fluids, being situated substantially at the other extremity of the tube and the second outlet passageway, for the other fluid, being situated laterally at an intermediate part of the tube; and a deflector sleeve situated within the tube connected to the tube wall between the inlet opening and the second outlet passageway and extending beyond the said second passageway and defining therein a channel for the flow of said mixture from the inlet opening into a region of the tube beyond the sleeve in isolation to said second passageway, both said passageways being in direct communication with the said region.

References Cited by the Examiner UNITED STATES PATENTS Angelo 233-15 Podbielniak a 233-15 Podbielniak et a1 233-15 Zabriskie 233-15 Van Dyck Fear et a1.

Benedict 208-324 Morin et a1. 208-324 Thurman 233-15 X Thurman 233-15 X Doyle et a1 233-15 Examiners. 

1. IN A CENTRIFUGAL APPARATUS FOR THE COUNTERCURRENT EXCHANGE OF AT LEAST PARTIALLY IMMISCIBLE PRINCIPAL FLUIDS OF DIFFERENT DENSITIES, THE COMBINATION OF: (A) A ROTOR INCLUDING AN ENCLOSING WALL AND AN AXIAL SHAFT MOUNTED FOR ROTATION, (B) A PLURALITY OF SPACED PARTITION WALLS WITHIN SAID ROTOR EXTENDING ANNULAR ABOUT SAID SHAFT AND DEFINING A SERIES OF CONTACTING COMPARTMENTS SITUATED AT PROGRESSIVELY DIFFERENT DISTANCES FROM SAID SHAFT, SAID PARTITION WALLS HAVING PASSAGES THERETHROUGH WHEREBY SAID COMPARTMENTS ARE IN INTERCOMMUNICATION, (C) A WALL STRUCTURE WITHIN SAID ROTOR DEFINING A CENTRIFUGAL SEPARATING CHAMBER WHICH EXTENDS RADIALLY THROUGHOUT A PLURALITY OF SAID INTERCOMMUNICATING COMPARTMENTS, (D) MEANS COMMUNICATING WITH THE OUTSIDE OF THE ROTOR AND WITH THE INTERIOR OF SAID CHAMBER FOR SUPPLYING A MIXTURE OF ONE OF SAID PRINCIPAL FLUIDS AND AN AUXILIARY FLUID WHICH IS SUBSTANTIALLY IMMISCIBLE THEREWITH AND HAS A DIFFERENT DENSITY FROM OUTSIDE THE ROTOR TO SAID SEPARATING CHAMBER FOR SEPARATION OF THE MIXTURE THEREIN BY CENTRIFUGAL FORCE, (E) SEPARATING OUTLET PASSAGEWAYS FROM SAID SEPARATING CHAMBER COMMUNICATING WITH THE INTERIOR OF SAID CHAMBER AT DIFFERENT RADIAL DISTANCES FROM SAID SHAFT FOR THE SEPARATE DISCHARGE FROM THE CHAMBER TO THE SEPARATED PRINCIPAL AND AUXILIARY FLUIDS, SAID PASSAGEWAYS BEING RESPECTIVELY FURTHER IN COMMUNICATION WITH SEPARATE, INTERCOMMUNICATING CONTACTING COMPARTMENTS SITUATED AT DIFFERENT RADIAL DISTANCES FROM SAID SHAFTS, (F) MEANS COMMUNICATING WITH THE INTERIOR AND EXTERIOR OF SAID ROTOR FOR SUPPLYING ANOTHER PRINCIPAL FLUID FROM OUTSIDE THE ROTOR TO A CONTACTING COMPARTMENT OTHER THAN THOSE MENTIONED IN (E), AND (G) SEPARATE DISCHARGE MEANS COMMUNICATING WITH INTERIOR AND EXTERIOR OF THE ROTOR FOR DISCHARGING RESPECTIVELY THE LESS DENSE FLUID FROM THE ROTOR INTERIOR NEAR THE RADIALLY INNER PORTION THEREOF AND THE DENSER FLUID FROM THE ROTOR INTERIOR NEAR THE RADIALLY OUTER PORTION THEREOF. 